The present invention relates generally to fire suppression systems and nozzles, and more particularly relates to clean agent gaseous fire suppression systems that use a liquefied compressed gas fire suppressant for suppressing fires and nozzles for such systems.
There are a wide variety of fire suppression systems commercially available today. One form of fire suppression system is known as a fixed xe2x80x9cclean agentxe2x80x9d gaseous fire suppression system. Clean agent fire extinguishing systems extinguish fires by creating a fire extinguishing atmosphere consisting of agent vapor or gas mixed with the air within the protected space. Clean agent systems are used in buildings and other such structures to suppress fires without water, powder or foam so not as to destroy or damage an enclosed area of the structure and/or equipment contained therein. Clean agent fire suppressants leave no residue upon evaporation. One common form of clean agent is a chemical that is in liquefied form under normal storage conditions but which may be vaporized to form a gaseous mixture with air which does not support combustion and extinguishes fires. Such liquefied-gas suppressants exists in liquid form when confined in a closed container but as a gas at ambient temperature and when not confined in a container.
Several years back, Halon 1301 (Bromotrifluoromethane) was the most common liquefied-gas fire suppressant used in fixed clean agent gaseous fire suppression systems. Halon 1301 quickly suppresses fires. Halon 1301 also has a very low boiling point (xe2x88x9257.8xc2x0 C.) such that once compressed liquid Halon 1301 is released into a room, it expands very rapidly to a complete gaseous state. Halon 1301 has a normal boiling point of xe2x88x9257.8xc2x0 C. (xe2x88x9272xc2x0 F.) and a vapor pressure of 14.4 bar (209 psia) at 20xc2x0 C. (68xc2x0 F.). As normally used in fire extinguishing systems containers of Halon 1301 were superpressurized with nitrogen, to facilitate pipe transport, to a total pressure at 21xc2x0 C. (70xc2x0 F.) of 24.8 bar (360 psig) or more. However, since 1993, Halon 1301 has now generally been prohibited from production under the terms of the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer. Due to the prohibition, the industry has had to look for viable alternative gas fire suppressants for the maintenance of existing systems and the design of new systems.
Today, the most widely used volatile liquefied-gas fire suppressant is 1,1,1,2,3,3,3-heptafluoropropane, or HFC-227ea. HFC-227ea has a normal boiling point of xe2x88x9216.4xc2x0 C. (2.5xc2x0 F.) and a vapor pressure of 3.9 bar (56.8 psia) at 20xc2x0 C. (68xc2x0 F.). This agent does not have the environmental problems associated with Halon 1301. In presently commercialized products, HFC-227ea agent is stored in steel cylinders with a substantial amount of dissolved compressed liquid nitrogen such that it is superpressurized to achieve a total pressure of either 360 psig or 600 psig. Upon the demand to suppress a fire, the solution of HFC-227ea and dissolved nitrogen is released into a pipe network and then discharged from a nozzle into the room of a building structure. The dissolved liquid nitrogen in the HFC-227ea plays an important role at this point. Namely, the dissolved liquid nitrogen expands rapidly upon being exposed to room pressure thereby breaking up the remaining HFC-227ea agent into tiny droplets that then boil to assume a gaseous state. This has occurred at a generally satisfactory rate for many systems but has also been subject to substandard results in some applications.
The substitution of this superpressurized HFC-227ea regime described above has certain limitations. In particular, the discharge of the suppresurized HFC-227ea agent from the steel cylinder into a network of pipes leading to the room of a building or other structure results in the agent and dissolved nitrogen being suddenly brought into a state of lower pressure. One result of this change is that some of the superpressurizing nitrogen gas, initially dissolved in the liquid HFC-227ea agent, comes out of solution and expands to a gaseous state in the pipe network. Clean agent and superpressurizing gas then flow through the pipe network as a two phase mixture. The two phase mixture consists of a liquid phase, with a reduced portion of the superpressurizing nitrogen gas still dissolved in the liquid agent, and a gas phase consisting of superpressurizing nitrogen gas with some agent vapor. One detrimental effect of the development of two-phase flow in a pipe system is that the mass flow rate of agent is limited as a consequence primarily due to the low average fluid density caused by the presence of low-density gas mixed with high-density liquid. Another inherent drawback is that HFC-227ea inherently has a higher boiling point than Halon 1301 and is subject to a slower vaporization. The dissolved nitrogen that expands rapidly upon discharge into the room has been useful but still has not achieved the superior vaporization characteristics previously experience for Halon 1301.
It is the general objective according to one aspect of the present invention to improve the improve the vaporization in fixed clean agent fire suppression systems in light of the fact that Halon 1301 is no longer a desirable clean agent due to environmental prohibition.
It is the general objective according to another aspect of the present invention to improve the flow rates of gas fire suppressants through the pipe network of fixed clean agent fire suppression systems to achieve an effective fire suppression system without the need to rely on Halon 1301.
In accordance with these and other objectives, the present invention is directed toward a clean agent fire suppression system for a room or other enclosed structure that includes an agent tank containing a clean agent, namely, a volatile liquefied gas fire suppressant, and a propellant tank of a compressed gas or liquefied compressed gas propellant stored separate from the gas fire suppressant. The propellant is stored in series such that it is capable of charging the pressure of the gas fire suppressant on demand. The system includes a plurality of nozzles arranged in the structure in spaced relation and a pipe network connecting the gas fire suppressant to the nozzles. A on/off system valve or other suitable valve controls fluid flow through the pipe network to selectively allow or prevent flow of the gas fire suppressant pushed by the propellant through the pipe network to the nozzles.
In contrast to prior systems where propellant and agent are stored together, the disclosed system may be in the form of a piston flow system wherein the propellant pushes the gas fire suppressant through the pipe network with little dissolution or mixing of the agent such that a liquid flow is maintained through the pipes, thereby providing a high mass flow rate. The disclosed system utilizes atomizing nozzles to fan the liquid gas fire agent out into small droplets that vaporize quickly into a gaseous state. The system is suitable as a retrofit system for prior Halon 1301 systems and can use the same existing pipe network of Halon 1301 systems thereby achieving significant cost savings while at the same time meeting industry standards of delivering the clean agent to the protected space in a time interval not exceeding 10 seconds.
The present invention also is directed toward a rapid atomizing nozzle that vaporizes the liquid clean agent quickly upon discharge. The nozzle comprises a nozzle body and a deflector body secured together in fixed relation. The nozzle body includes an inlet port through the nozzle body along an axis and a conical flow surface extending radially outwardly from the inlet port. The deflector body includes a conical deflector surface in spaced fixed relation to the conical flow surface such that a conical flow passage is formed between the nozzle body and deflector body. The conical flow passage extends radially outward to a circumferential outlet slot that spreads the liquid clean agent out into a thin liquid conical fan that breaks up into small droplets that atomize more quickly. The atomizing nozzle is also beneficial for existing superpressurized clean agent fire suppression systems where the fire suppression gas is stored in a cylinder with dissolved compressed nitrogen.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.